Node JS with typescript failing to catch express errors using middleware

Question

I need all the errors returning from api to be is a specific json format. So when I add the middleware error handling logic to my Node JS typescript app to catch route errors, it does not work.

My app.ts file:

import express, { Application, Request, Response, NextFunction } from 'express';
import routes from './src/start/routes';
import cors from 'cors';
require('dotenv').config();

const app: Application = express();
app.use(express.json());
app.use(cors());
app.use(express.urlencoded({ extended: false }));
app.use('/', require('./src/routes/api.route'));
app.use('/api', routes);

//Error Handler

app.use((error: any, req: Request, res: Response, next: NextFunction) => {
    return res.status(500).json({
        status: 500,
        success: 0,
        message: 'Error',
        error: ['Server error.'],
        data: {}
    });
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => console.log(`http://localhost:${PORT}`));

So if I enter a wrong route for example, I get the error 'Cannot GET /WrongRoute' in a single string format and not in the json format that I need. What to do?

Answer 1

The Express 404 error handler is of this form:

app.use((req, res, next) => {
  res.status(404).send({msg: "404 route not found"});
});

You just make sure this is AFTER any routes you have defined.

---

Your four parameter error handler:

app.use((error, req, res, next) => {
     // put error handling code here
});

Is for a different type of error where a specific Error object has already been created by the error such as a synchronous exception occurring in a route or someone calling next(err). This four argument error handler does not come into play just because no route matched an incoming request.